Shielded probe apparatus for probing semiconductor wafer

ABSTRACT

A shielded probe apparatus is provided with a shielded probe and a tri-axial cable that are electrically connected within a shielded chassis. The shielded probe apparatus is capable of electrically testing a semiconductor device at a sub 100 fA operating current and an operating temperature up to 300C.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This is a utility patent application which claims priority ofU.S. provisional patent application Serial No. 60/392,394, filed Jun.28, 2002; subject matter of which is incorporated herewith by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to semiconductor testequipment, and more particularly, to a shielded probe used insemiconductor test equipment for electrically probing devices on asemiconductor wafer.

BACKGROUND OF THEE INVENTION

[0003] The semiconductor industry has a need to access many electronicdevices on a semiconductor wafer. As the semiconductor industry growsand devices become more complex, many electrical devices, most commonlysemiconductor devices, must be electrically tested, for example, forleakage currents and extremely low operating currents. These currentsare often below 100 fA. In addition, the currents and devicecharacteristics are often required to be evaluated over a widetemperature range to understand how temperature affects a device. Toeffectively measure at currents below 100 fA, a measurement signal mustbe isolated from external electrical interference, leakage currentsthrough the dielectric material, parasitic capacitance, triboelectricnoise, piezoelectric noise, and dielectric absorption, etc.

[0004] At present, semiconductor test equipment has been designed to tryto prevent the above described interference or noise, etc. at a testequipment side, by driving a guard layer of a tri-axial cable at thesame potential as a center signal conductor of the tri-axial cable. Theouter shield of the tri-axial cable is grounded to the test equipment.It is desired that external electrical interference, leakage currentsthrough the dielectric material, parasitic capacitance, triboelectricnoise, piezoelectric noise, and dielectric absorption are significantlyreduced or eliminated.

[0005] Also, because of the materials characteristics of dielectrics, itis often difficult to test characteristics of semiconductor devices in awide operating temperature range.

[0006] Accordingly, there is a need for improved semiconductor testequipment for electrically probing semiconductor devices at low currentsand over a wide temperature range.

SUMMARY OF THE INVENTION

[0007] To solve the above and the other problems, the present inventionprovides a shielded probe apparatus connected to semiconductor testequipment wherein the shielded probe apparatus includes a shielded probeand a tri-axial cable. The shielded probe includes a probe pin typicallya metal wire made of electrochemically etched tungsten or the like. Theprobe pin is shielded and configured to electrically connect to thetri-axial cable for electrically probing semiconductor devices at lowcurrents and over a wide operating temperature range.

[0008] In one embodiment, the shielded probe apparatus is capable ofelectrically testing a semiconductor device at a sub 100 fA operatingcurrent and an operating temperature up to 300C.

[0009] In one embodiment, the tri-axial cable is connected to theshielded probe within a shielded chassis. The shielded probe includes aprobe pin surrounded by a dielectric layer, an electrically conductiveguard layer, and an optional protective dielectric layer. The tri-axialcable includes a center signal conductor surrounded by a dielectriclayer, a conductive coating to reduce triboelectric effects, aconductive guard layer, a second dielectric layer, a conductive shieldlayer, and a protective cover. The tri-axial cable is connected to theshielded probe by electrically connecting the center signal conductor tothe probe pin, such as by using high temperature to solder/braze orcrimp the probe pin on the center signal conductor and in a preferredembodiment, shrink-tube, crimp, or clamp the tri-axial cable and theshielded probe to electrically connect the guard layer of the tri-axialcable to the conductive guard layer of the shielded probe. It will beappreciated that other suitable means of electrically connecting thecenter signal conductor and the probe pin and electrically connectingthe guard layer of the tri-axial cable and the conductive guard layer ofthe shielded probe can be used without departing the scope of theprinciples of the invention.

[0010] Accordingly, the dielectric layer, the conductive guard layer,and the optional second dielectric layer of the shielded probesignificantly reduce external electrical interference and allow theprobe pin to test and measure small currents, such as below 100 fA.Also, the shielded probe is allowed to test the characteristics of thesemiconductor devices not only in a low operating temperature but alsoin a high operating temperature, i.e. a wide operating temperature rangeby using flexible dielectric materials compatible with hightemperatures. In addition, the connection between the guard layer of thetri-axial cable and the conductive guard layer of the shielded probe andthe connection between the center signal conductor and the probe pinhelp prevent leakage currents through the dielectric materials,parasitic capacitance, piezoelectric noise, and dielectric absorption.Further, the conductive coating between the dielectric layer and theguard layer of the tri-axial cable significantly reduces and/oreliminates triboelectric noise.

[0011] These and other features and advantages of the present inventionwill become apparent to those skilled in the art from the followingdetailed description, wherein it is shown and described illustrativeembodiments of the invention, including best modes contemplated forcarrying out the invention. As it will be realized, the invention iscapable of modifications in various obvious aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a cross-sectional view of one embodiment of a typicaltri-axial cable used in semiconductor test equipment.

[0013]FIG. 2A is one embodiment of a shielded probe in accordance withthe principles of the present invention.

[0014]FIG. 2B is a cross-sectional view of one embodiment of theshielded probe, as shown in FIG. 2A, in accordance with the principlesof the present invention.

[0015]FIG. 3 is a schematic view of one embodiment of a shielded probeapparatus used in semiconductor test equipment, in accordance with theprinciples of the present invention.

[0016]FIG. 4A is a cross-sectional view of one embodiment of a tri-axialcable of the shielded probe apparatus, along line 4A-4A in FIG. 3, inaccordance with the principles of the present invention.

[0017]FIG. 4B is a cross-sectional view of one embodiment of thetri-axial cable of the shielded probe apparatus, along line 4B-4B inFIG. 3, in accordance with the principles of the present invention.

[0018]FIG. 4C is a cross-sectional view of one embodiment of thetri-axial cable connected to the shielded probe of the shielded probeapparatus, along line 4C-4C in FIG. 3, in accordance with the principlesof the present invention.

[0019]FIG. 5 is a side cross-sectional view of one embodiment of thetri-axial cable connected to the shielded probe of the shielded probeapparatus, in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In the following description of a preferred embodiment, referenceis made to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

[0021] For purposes of explanation, numerous specific details are setforth in the following description in order to provide a thoroughunderstanding of the present invention. However, it will be evident toone of ordinary skill in the art that the present invention may bepracticed without some of these specific details. In other instances,well-known structures and devices are shown in block diagram form inorder to facilitate description.

[0022] The present invention utilizes the center signal conductor, guardlayer, and ground of a tri-axial cable provided by semiconductor testequipment or tester to electrically isolate a probe pin enabling the lowcurrent measurements, for example, sub 100 fA measurements. The presentinvention also allows the tester to electrically probe devices over awide operating temperature range, not only at a low operatingtemperature but also a high operating temperature, e.g. an operatingtemperature up to 300C.

[0023]FIG. 1 illustrates a cross-sectional view of a typical tri-axialcable 100 with a center signal conductor 102 surrounded by a firstdielectric layer 104. The first dielectric layer 104 is surrounded by aguard layer 106. The guard layer 106 is electrically conductive and issurrounded by a second dielectric layer 108. A conductive coating ordispersion layer 107 is sandwiched between the first dielectric layer104 and the guard layer 106. The tri-axial cable 100 also includes ashield layer 110 and a protective dielectric cover layer 111 to isolatethe tri-axial cable from external interference or other environmentalhazard.

[0024] It will be appreciated that the term “surrounded” used herein andhereinafter is not limited to describe one layer being surrounded byanother layer in its entirety. In some embodiments, one layer may bepartially surrounded by another layer, whereas in other embodiments, onelayer may be entirely surrounded by another layer.

[0025]FIGS. 2A and 2B illustrate a shielded probe 112 which includes aprobe pin 114. The configuration of the probe pin 114 can be varied, acouple of which are disclosed in a pending utility patent applicationSer. No. 09/730,130, filed on Dec. 4, 2000, which is aContinuation-In-Part (CIP) patent application of Ser. No. 09/021,631,filed on Feb. 10, 1998, which are incorporated herewith by references.

[0026] The probe pin 114 is surrounded by a first dielectric layer 116preferably made of a thin, flexible high temperature dielectricmaterial, such as poly (tetrafluoro-p-xylylene), a class of polymersknown as parylene. The first dielectric layer 116 is preferably coatedon the probe pin by a physical or chemical-vapor deposit (PVD or CVD)method. It will be appreciated that other suitable flexible hightemperature dielectric materials, such as epoxies, or other suitablecoating methods can be used within the scope of the present invention.

[0027] The probe pin 114 with the dielectric layer 116 is preferablysputter-coated with an electrically conductive guard layer 118. Theconductive guard layer 118 is preferably made of gold. It will beappreciated that other suitable conductive coating materials and coatingmethods can be used without departing from the scope of the presentinvention.

[0028] A second dielectric layer 122 may be provided outside of theconductive guard layer 118. The second dielectric layer 122 is anoptional protective coating which provides protection layer for theconductive guard layer 118. The second dielectric layer 122 ispreferably made of a thin, flexible high temperature dielectricmaterial, such as polyamide. It will be appreciated that other suitableflexible high temperature dielectric materials can be used within thescope of the present invention.

[0029] As shown in FIG. 3, a shielded probe apparatus 124, in accordancewith the principles of the present invention, includes an electricallyshielded chassis 126 and a ceramic assembly 128 for electrically probingsemiconductor devices (not shown). A tri-axial cable 130 ofsemiconductor test equipment is inserted into the shielded chassis 126at one end 132 and connected to the shielded probe 112 at the other end134.

[0030] As shown in FIG. 4A, the tri-axial cable 130 includes a centersignal conductor 136 on which testing signals are carried from the testequipment to the shielded probe 112. The center signal conductor 136 issurrounded by a first dielectric layer 138 preferably made of hightemperature PTFE (Teflon). The first dielectric layer 138 is surroundedby an electrically conductive coating or dispersion layer 140. Theconductive coating or dispersion layer 140 is sandwiched between thefirst dielectric layer 138 and an electrically conductive guard layer142 to reduce triboelectric effects. In a testing operation, the guardlayer 142 is driven at the same potential as the center signal conductor136 such that the capacitance between the guard layer 142 and the centersignal conductor 136 is eliminated. Accordingly, the parasiticcapacitance is eliminated, and current leakage is prevented.

[0031] An optional second dielectric layer 144 may be provided outsideof the guard layer 142. A shield 146 and a protective dielectric cover(not shown) are provided outside of the guard layer 142 and/or theoptional second dielectric layer 144 to isolate the tri-axial cable 130from external interference.

[0032] As shown in FIG. 3, the tri-axial cable 130 is inserted into thechassis 126 where the shield 146 and the protective dielectric cover(not shown) of the tri-axial cable 130 are stripped away andelectrically connected to the ground. FIG. 4B illustrates across-sectional view of the cable 130 along line 4B-4B in FIG. 3. Theoptional second dielectric layer 144 may extend to the shielded probe112 or terminate at the chassis' sidewalls.

[0033]FIG. 4C illustrates a cross-sectional view (along line 4C-4C inFIG. 3) where the tri-axial cable 130 is connected to the shielded probe112. FIG. 5 illustrates a side cross-sectional view of one embodiment ofthe tri-axial cable 130 connected to the shielded probe 112 of theshielded probe apparatus 124. The tri-axial cable 130 is attached to theshielded probe 112, preferably by using high temperature to solder/brazeor crimp the probe pin 114 on the center signal conductor 136, andshrink-tube, crimp, or clamp the tri-axial cable 130 and the shieldedprobe 112 into a shrink tube layer 148 to electrically connect the probepin 114 to the center signal conductor 136. A second shrink tube layer149 electrically connects the guard layer 142 of the tri-axial cable 130to the conductive guard layer 118 of the shielded probe 112. It will beappreciated that other suitable means of electrically connecting thecenter signal conductor and the probe pin and electrically connectingthe guard layer of the tri-axial cable and the conductive guard layer ofthe shielded probe can be used without departing the scope of theprinciples of the invention.

[0034] In one embodiment, the optional second dielectric layer 144 ofthe tri-axial cable 130 and/or the optional second dielectric layer 122of the shielded probe may be shrink-tubed by folding back and over (notshown) the tri-axial cable 130 and the shielded probe 112, respectively,so as to help retain the physical connection between the shielded probe112 and the tri-axial cable 130.

[0035] Further referring to FIG. 3, a probing end of the shielded probe112 is inserted into a hole and a slot of the high temperature ceramicassembly 128 or other suitable high temperature-resistant material, asdescribed in the pending utility patent application Ser. No. 09/730,130,filed on Dec. 4, 2000, which is a Continuation-In-Part (CIP) patentapplication of Ser. No. 09/021,631, filed on Feb. 10, 1998, which areincorporated herewith by references.

[0036] Further in one embodiment, the probe pin 114 is made ofelectrochemically etched tungsten or other suitable materials. Thediameter of the probe pin 114 is preferably in a range of 0.1 mm to 0.25mm. It will be appreciated that the materials, diameter, andconfiguration of the probe pin 114 can be varied without departing fromthe principles of the present invention.

[0037] From the above description and drawings, it will be understood bythose of ordinary skill in the art that the particular embodiments shownand described are for purposes of illustration only and are not intendedto limit the scope of the present invention. Those of ordinary skill inthe art will recognize that the present invention may be embodied inother specific forms without departing from its spirit or essentialcharacteristics. References to details of particular embodiments are notintended to limit the scope of the invention.

What is claimed is:
 1. A shielded probe apparatus for testing asemiconductor device, comprising: a shielded probe for probing thesemiconductor device; a tri-axial cable coupled to a test equipment; ashielded chassis; and the tri-axial cable and the shielded probe beingconfigured and arranged to connect to each other within the shieldedchassis.
 2. The apparatus of claim 1, wherein the shielded probecomprises: a probe pin; a dielectric layer, the probe pin beingsurrounded by the dielectric layer; and a conductive guard layer, thedielectric layer being surrounded by the conductive guard layer.
 3. Theapparatus of claim 2, wherein the tri-axial cable comprises: a centersignal conductor; a dielectric layer, the center signal conductor beingsurrounded by the dielectric layer; a conductive layer, the dielectriclayer being surrounded by the conductive layer; a guard layer, theconductive layer being surrounded by the guard layer; a seconddielectric layer, the guard layer being surrounded by the seconddielectric layer; a shield, the second dielectric layer being surroundedby the shield; and a protective cover, the shield being surrounded bythe protective cover.
 4. The apparatus of claim 2, wherein the shieldedprobe further comprises a second dielectric layer, the conductive guardlayer being surrounded by the second dielectric layer.
 5. The apparatusof claim 3, wherein the probe pin and the center signal conductor areelectrically connected to each other.
 6. The apparatus of claim 5,wherein the probe pin is electrically connected to the center signalconductor.
 7. The apparatus of claim 5, further comprising a shrink tubeto shrink-tube the probe pin and the center signal conductor.
 8. Theapparatus of claim 3, wherein the conductive guard layer of the shieldedprobe and the guard layer of the tri-axial cable are electricallyconnected to each other.
 9. The apparatus of claim 8, further comprisinga second shrink tube to shrink-tube the conductive guard layer and theguard layer.
 10. The apparatus of claim 3, wherein the guard layer ofthe tri-axial cable is driven to the same potential as the center signalconductor, and the shield of the tri-axial cable is grounded to theshielded chassis.
 11. A shielded probe apparatus, capable ofelectrically testing a semiconductor device at a sub 100 fA operatingcurrent and an operating temperature up to 300C, comprising a shieldedprobe and a tri-axial cable that are electrically connected within ashielded chassis.
 12. The apparatus of claim 11, wherein the shieldedprobe comprises: a probe pin; a dielectric layer, the probe pin beingsurrounded by the dielectric layer; and a conductive guard layer, thedielectric layer being surrounded by the conductive guard layer.
 13. Theapparatus of claim 12, wherein the tri-axial cable comprises: a centersignal conductor; a dielectric layer, the center signal conductor beingsurrounded by the dielectric layer; a conductive layer, the dielectriclayer being surrounded by the conductive layer; a guard layer, theconductive layer being surrounded by the guard layer; a seconddielectric layer, the guard layer being surrounded by the seconddielectric layer; a shield, the second dielectric layer being surroundedby the shield; and a protective cover, the shield being surrounded bythe protective cover.
 14. The apparatus of claim 12, wherein theshielded probe further comprises a second dielectric layer, theconductive guard layer being surrounded by the second dielectric layer.15. The apparatus of claim 13, wherein the probe pin and the centersignal conductor are electrically connected to each other.
 16. Theapparatus of claim 15, wherein the probe pin is electrically connectedto the center signal conductor.
 17. The apparatus of claim 15, furthercomprising a shrink tube to shrink-tube the probe pin and the centersignal conductor.
 18. The apparatus of claim 13, wherein the conductiveguard layer of the shielded probe and the guard layer of the tri-axialcable are electrically connected to each other.
 19. The apparatus ofclaim 18, further comprising a second shrink tube to shrink-tube theconductive guard layer and the guard layer.
 20. The apparatus of claim13, wherein the guard layer of the tri-axial cable is driven to the samepotential as the center signal conductor, and the shield of thetri-axial cable is grounded to the shielded chassis.